Transverse-electric transverse-magnetic (TE-TM) mode conversion in a magnetooptic waveguide by use of a reversal of a coupling coefficient is addressed. A transmission matrix treatment for a class of coupled mode systems is used for the design of an experimental arrangement. The reversal method used is proved qualitatively to be advantageous to improve an incomplete conversion by the experiment using a (YLa)3 (FeGa)5O12 rib channel waveguide at 1.15 μm wavelength. The method was previously investigated with a slab waveguide by the authors, and its usefulness was qualitatively confirmed. In the present work attention is paid to quantitative verification